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Difficulty: EasyContinuous and Discontinuous Variation

Which of the following characteristics is a defining feature of discontinuous variation in a biological population?

  1. A
    A smooth gradient of phenotypes across a normal distribution curve
  2. B
    Significant modification of the phenotypic expression by environmental conditions
  3. The presence of clear-cut, distinct phenotypic categories with no intermediate formsAnswer
  4. D
    Genetic control by many additive genes acting together polygenically

Answer

The presence of clear-cut, distinct phenotypic categories with no intermediate forms
Discontinuous variation produces non-overlapping phenotypic classes with distinct differences and no intermediate stages between them. Examples include human ABO blood groups, ability to roll the tongue, and presence or absence of horns in cattle.

Step-by-Step Solution

1
Define discontinuous variation in genetic terms.
Discontinuous variation refers to phenotypic traits that are split into distinct, non-overlapping classes.
Understanding the core definition differentiates it from continuous variation.
2
Evaluate the option choices against key features of discontinuous variation.
Discontinuous traits are typically monogenic (controlled by one gene), unaffected by environment, and show discrete phenotypic categories without intermediate states.
Traits like blood groups or sex determination are either present or absent in fixed categories.

Key Concept

Discontinuous Variation Features
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Topics

Continuous and Discontinuous Variation

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